Image processing apparatus and image processing method

ABSTRACT

An image processing apparatus executes an error diffusion process to multivalue image data consisting of a plurality of density components. A first processor executes the error diffusion process by changing at least one of a quantization threshold value and a quantization diffusion coefficient which are used for the error diffusion process based on a value of the multivalue image data of the density components or a value calculated from the multivalue image data value. A second processor executes the error diffusion process by setting the quantization threshold value and the quantization diffusion coefficient which are used for the error diffusion process into fixed values. An error diffusion processing controller controls to execute the error diffusion process to at least one color among the density components by the first processor and execute the error diffusion process to other density components by the second processor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a data process of an image processingapparatus for executing an error diffusion process to multivalue imagedata comprising a plurality of density components and outputting aresult of the error diffusion process.

[0003] 2. Related Background Art

[0004] Hitherto, a recording apparatus which can record an image ontorecording paper on the basis of image data processed by such a kind ofimage processing apparatus has been proposed.

[0005] As recording elements of such a recording apparatus, variousrecording elements according to recording systems can be used. Forexample, in the case of an ink jet recording system, an ink jetrecording element serving as a nozzle for emitting ink from an inkemitting port can be used. In the case of the ink jet recording system,not only the recording ink can be emitted, a picture quality improverfor making a color material in the recording ink insoluble oraggregating it can be also emitted.

[0006] As an image process in the image processing apparatus asmentioned above, a quantization image process for quantizing multivaluegradation data by an error diffusion method in accordance with variousmethods is executed.

[0007] For example, in the image processing apparatus to execute thequantization image process for quantizing the multivalue gradation databy the error diffusion method, in the recording apparatus to which theimage processing apparatus can be applied, when the inputtedmultigradation data is outputted to an imaging apparatus which canexpress it only by two gradations of 0 and 1 or by gradations of thenumber which is smaller than the number of gradations of the input data,the data is falsely expressed by a gradation halftone process.

[0008] As a method by which density characteristics of an inputted imagecan be maintained and high picture quality can be obtained, an errordiffusion method (refer to a literature (Loyd. R. W. and L. Steinberg,“Adoptive Algorithm for Spatial Greyscale,”, SID Int. Sym., Digest ofTech Papers, 36, 37, 1975)) has been known.

[0009] According to such a method, a density difference between a pixeldensity of the input side and a pixel density of the output side whichis outputted as a result of a comparison between the pixel density ofthe input side and a threshold value (such a threshold value ishereinafter called a quantization threshold value) is calculated. Aspecific weight is added to such a density difference and, thereafter,the resultant density difference is distributed to neighboring pixels. Avalue of such a weight (for every pixel) to the neighboring pixels or aset of such values is hereinafter called an error diffusion coefficient.By executing such a pseudo gradation expressing process as mentionedabove, substantial resolution of the image which is outputted does notdeteriorate but the image can be outputted at high quality.

[0010] In association with the realization of high performance of recentPCs (personal computers), as methods of improving the error diffusionmethod and realizing the higher picture quality, the methods disclosedin JP-A-H10-200724, JP-A-2002-51212, JP-A-H8-46784, JP-A-H8-307680, andthe like can be mentioned. Those prior arts are mainly classified intothe following two kinds of processes.

[0011] 1) As a process regarding modulation of the error diffusioncoefficient, there is a method disclosed in JP-A-H10-200724. The methodis characterized in that when a value of an input signal indicates ahighlight image, the error diffusion coefficient whose weight in themain scanning direction is large is used, that is, the error diffusioncoefficient different from that of a normal image portion is used for ahighlight image portion.

[0012] In JP-A-2002-51212, the error diffusion coefficient is set for avalue of an error which is caused at the time of quantization.

[0013] 2) As a process regarding modulation of the quantizationthreshold value, there is a method disclosed in JP-A-H8-46784. Accordingto the method, a binarizing process is executed on the basis of avariable threshold value determined on the basis of an input density ofa target pixel. According to a technique disclosed in JP-A-H8-307680,random number noises according to the input signal are added to thethreshold value.

[0014] According to the error diffusion method mentioned above, a fixedvalue is used as an error diffusion coefficient or a quantizationthreshold value. On the other hand, according to those improved errordiffusion methods, the error diffusion coefficient or the thresholdvalue is made variable in accordance with a value regarding a feature ofan original image such as input data, quantization error, or the like.

[0015] By those methods, reduction in (1) delay of dot appearance in thehighlight portion and (2) occurrence of a periodic dot pattern at aspecific gradation which became the problems in the error diffusionmethod mentioned above is realized. A large effect of improvement of thepicture quality is obtained particularly with respect to the delay ofthe dot appearance in the highlight portion and occurrence of a dotchain pattern.

[0016] Hereinbelow, the error diffusion method regarding the aboveprocess 1) is called a diffusion coefficient modulation type errordiffusion method and the error diffusion method regarding the aboveprocess 2) is called a threshold value modulation type error diffusionmethod. The inherent error diffusion method whereby the modulation ofthe diffusion coefficient is not executed is called a diffusioncoefficient fixed type error diffusion method for convenience and theerror diffusion method whereby the modulation of the threshold value isnot executed is called a threshold value fixed type error diffusionmethod for convenience.

[0017] In recent years, the ordinary user can handle digital data ofhigh picture quality in association with the spread of PCs of highperformance and digital cameras of high precision. Consequently, a printof higher picture quality than the conventional one has been realized byusing an ink jet recording apparatus or the like. It is forecasted thata demand for realizing the even higher picture quality increases in thefuture. Techniques to realize the high picture quality as mentionedabove will become more and more important.

[0018] Meanwhile, in recent years, a demand for recording digital imagedata onto a medium such as paper or the like without using the PC isalso increasing. First, a “WebTV” (registered trademark) system and asystem such as “SetTopBox” or the like in which an Internet function isannexed to an ordinary television can be mentioned as systems which makethe Internet use handy and easy. A demand for printing out the digitalimage data by what is called a (Non-PC) system which does not use the PCis also increasing.

[0019] In association with the spread of the digital cameras, a productwhich directly reads out stored data of the digital camera from a cardthrottle provided for a printer main body via a recording medium such asa compact flash (registered trademark) (CF) card or the like anddirectly performs printing without an intervention of a host PC has beenrealized.

[0020] Further, a product which can execute a direct printing processsuch that image data of the digital camera or the like is directlytransmitted to the printer side by using a communication form of auniversal serial bus (USB) or the like without an intervention of therecording medium such as a CF card or the like and recorded has alsobeen realized.

[0021] In the invention, those products are called photodirect printersand a technique for realizing those functions is called a photodirectprinting technique hereinbelow.

[0022] According to those photodirect printers, a controller unit tocontrol the printer is provided in the printer and an image processingunit to execute predetermined processes to an image is also provided inthe printer. The photodirect printers are generally constructed so thatprocesses such as rendering, rasterization, color conversion,quantization, generation of a command to control the printing, and thelike of the image which are executed on the host PC side in theconventional printers are executed by the image processing unit and theformed data is sent to a printer engine unit.

[0023] The printer engine unit reads out the formed data and interpretsthe print control command and the print data as necessary. The printerengine unit makes mechanical control such as paper feed, carriagemovement, and the like which are necessary for recording the image ontoan actual non-recording medium and also makes control such as applyingof a recording head drive pulse, transmission of the data to a recordinghead, and the like.

[0024] Those controls which are made by the printer engine unit aresubstantially the same as those which are made when the printer engineunit receives data from the conventional host PC.

[0025] Recently, in association with the realization of the highperformance of the PCs, a printer driver has been designed so that itsprocesses on the PC are executed in a manner such that a high enoughprocessing speed and high enough picture quality can be realized in anenvironment such that the PC has a memory of a large enough storingcapacity of a unit of tens of megabytes and a high-speed CPU of a GHzunit.

[0026] In the Non-PC system or photodirect printer system whose demandhas been increased in recent years as mentioned above, the memory of thelarge enough storing capacity and the high-speed CPU are not alwaysprovided for the image processes. In fact, in the Non-PC system orphotodirect printer system which has been produced as a product in themarket, a printing ability, particularly, speed performance of theprinter engine unit cannot be effectively used due to a cause of aprocessing load in the controller unit.

[0027] In such an environment, in the case of using the various improvederror diffusion methods mentioned above, there are the followingproblems.

[0028] First, if the processes of the printer driver which are executedon the PC with performance higher than that of the specification of aprinter controller are executed as they are in the controller unit ofthe photodirect printer, a load of the image processing unit increases.Thus, a image recording speed deteriorates.

[0029] Particularly, the processing load in an error diffusionprocessing unit in the whole image process in the printer is generallyequal to 30 to 50%. Further, the more the processing load in the variousimproved error diffusion methods increases, the more an influence on thewhole system increases.

[0030] For example, in the technique disclosed in JP-A-10-200724mentioned above, it is necessary that the gradation distributing unitcertainly makes the discrimination about the highlight portion. Sincethose processes are executed to the whole inputted image, the load ofthe discriminating process directly influences the performance of thewhole printer.

[0031] Also in the other error diffusion method mentioned above, since aprocess to change parameters every processing pixel is necessary, theload also increases.

[0032] In recent color ink jet printers, there are many such products inwhich the recording is executed by using not only the ink of four colorsof C (cyan), M (magenta), Y (yellow), and K (black) but also the ink ofcolors of C (cyan) for a low density, M (magenta) for a low density, R(red), G (green), and B (blue) or the recording is executed byselectively using different liquid droplet amounts even in the case ofthe ink of the same color. With respect to those colors as well,quantization is executed separately from that for four fundamentalcolors of CMYK and an image is formed.

[0033] However, the concept of the colors is not disclosed in theOfficial Gazettes disclosing the foregoing diffusion coefficientmodulation type error diffusion method and the threshold valuemodulation type error diffusion method mentioned above. That is, aconcept that a proper data process is executed in accordance with acomponent such as color, liquid droplet type, or the like to bequantized (hereinafter, such a component is referred to as aquantization component or a density component) is not presumed.Naturally, a situation such that if the error diffusion process isexecuted without considering those components, a processing efficiencyof the print data deteriorates, a print result of high picture qualitycannot be obtained at a high speed, and the like is considered.

SUMMARY OF THE INVENTION

[0034] The invention relates to an image processing apparatus forexecuting an error diffusion process to multivalue image data consistingof a plurality of density components and this apparatus comprises: firstprocessing means for executing the error diffusion process by changingat least one of a quantization threshold value and a quantizationdiffusion coefficient which are used for the error diffusion process onthe basis of a value of the multivalue image data of the densitycomponents or a value calculated from the multivalue image data value;second processing means for executing the error diffusion process bysetting the quantization threshold value and the quantization diffusioncoefficient which are used for the error diffusion process into fixedvalues; and error diffusion processing control means for making controlto execute the error diffusion process to at least one color among theplurality of density components by the first processing means andexecute the error diffusion process to other density components by thesecond processing means.

[0035] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a diagram for explaining a construction of a printingapparatus to which an image processing apparatus showing the firstembodiment of the invention can be applied;

[0037]FIG. 2 is a flowchart showing an example of a first dataprocessing procedure in the image processing apparatus according to theinvention;

[0038]FIG. 3 is a diagram for explaining a relation between input imagedata and the number of ink droplets in the image processing apparatusaccording to the invention;

[0039]FIG. 4 is a flowchart showing an example of a second dataprocessing procedure in the image processing apparatus according to theinvention;

[0040]FIG. 5 is a flowchart showing an example of a third dataprocessing procedure in the image processing apparatus according to theinvention; and

[0041]FIG. 6 is a diagram for explaining a memory map of a storingmedium for storing various data processing programs which can be readout by the image processing apparatus according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Embodiments of the invention will be described hereinbelow withreference to the drawings.

[0043] First Embodiment

[0044]FIG. 1 is a diagram for explaining a construction of a printingapparatus to which an image processing apparatus showing the firstembodiment of the invention can be applied. Although a case of using anink jet printer as a printing apparatus will be described here, theinvention can be applied to any type of image forming system such as inkjet system, electrophotographic system, thermal transfer system, or thelike.

[0045] A controller 211, a data transmitting unit 219, a storing area220, and the like exist in a print control apparatus 210 shown in FIG.1.

[0046] A cache method determining unit 212, a print image obtaining unit213, color correction processing means 214, color conversion processingmeans 215, a quantizing unit 216, and a print data forming unit 217exist in the controller 211.

[0047] A printer engine 230 is constructed by a data receiving unit 231,a data printing unit 232 having an ink jet head which can emit inkdroplets of, for example, six colors, and the like. The print controlapparatus 210 and the printer engine 230 are connected by an interface.

[0048] A color correction processing unit 2140 and a color correctioncache processing unit 2141 exist in the color correction processingmeans 214. A color conversion processing unit 2150 and a colorconversion cache processing unit 2151 exist in the color conversionprocessing means 215.

[0049] The above construction will be described in detail hereinbelow.First, in controller 211, whether a cache for a color process and acolor conversion is used or not is determined as a pre-process by thecache method determining unit 212, which will be explained hereinlater.

[0050] When an actual printing process is started, an image serving as aprint target is obtained by the print image obtaining unit 213 and thecolor correction processing means 214 is executed to the obtained image.The color correction processing means 214 is constructed by the colorcorrection processing unit 2140 and the color correction cacheprocessing unit 2141. When a color correction cache is invalid or evenif it is valid, if the target pixel is not cached, a color correctingprocess is executed.

[0051] The color conversion processing means 215 is constructed by thecolor conversion processing unit 2150 and the color conversion cacheprocessing unit 2151. Processes are executed in a manner similar to thecase of the color correction. The data which passed through the colorconversion processing unit 2150 is subjected to an error diffusionprocess and a dither process by the quantizing unit 216 and convertedinto quantized data that can be handled by the printer. The print dataforming unit 217 converts the quantized data into printer print data andtransmits it to the printer via a print data output unit 218.

[0052] In the color correction cache processing unit 2141 and the colorconversion cache processing unit 2151, a cache table, which will beexplained hereinlater, is stored in the storing area 220 and used.

[0053] The data receiving unit 231 in the printer engine 230 receivesthe data transmitted from the data transmitting unit 219 in the printcontrol apparatus 210 and prints by using the data printing unit 232.The operating processes in the hardware regarding the print controlapparatus has been described in detail above.

[0054] The image processing apparatus (example in which the invention isapplied to the print control apparatus in FIG. 1) constructed asmentioned above is an image processing apparatus for executing the errordiffusion process to multivalue image data consisting of a plurality ofdensity components and outputting a result of the error diffusionprocess.

[0055] The data forming method by the quantizing unit 216 shown in FIG.1 will be described with reference to FIGS. 2, 3, and the like.

[0056] In the embodiment, an example in which the data printing unit 232of the printer engine 230 records and processes the image data by liquiddroplets of cyan (sC) and magenta (sM) of small liquid droplet amountsin addition to liquid droplets of black (K), cyan (C), magenta (M), andyellow (Y) of ordinary liquid droplet amounts is used. This means thatthere are six kinds (corresponding to the number of colors of inks ofthe ink jet head) of quantization components to be quantized everycolor.

[0057] A schematic procedure of the actual image processes is asfollows.

[0058] First, before the data is sent to the quantizing unit 216, thecolor converting unit executes a conversion (RGB→R′G′B′) for matching acolor gamut RGB in a data format of an original image (for example, RGB)with a color gamut R′G′B′ which can be outputted by the printer.

[0059] After that, the converted color gamut R′G′B′ is converted into anoutput level value of each recording component (K, C, M, Y, sC, sM) inthe printer.

[0060] The data of the output level value is transferred to thequantizing unit 216 every quantization component.

[0061]FIG. 2 is a flowchart showing an example of the first dataprocessing procedure in the image processing apparatus according to theinvention. This process is executed by the quantizing unit 216 shown inFIG. 1. S1001 to S1007 denote processing steps, respectively.

[0062] First, a color component of the relevant line to be quantized isinputted (step S1001).

[0063] What is the quantization component of the relevant line isdiscriminated (step S1002). If the quantization component of therelevant line is sC (or sM), step S1003 follows and the diffusioncoefficient modulation type error diffusion process is executed.

[0064] In this case, it is assumed that the error diffusion coefficientof the highlight portion is set to a ratio different from that of theerror diffusion coefficient of the normal portion.

[0065] The data of the relevant quantization component of one line isformed (step S1004). After that, the processing routine advances to theprocess for the next color (step S1005).

[0066] If a result of the discrimination in step S1002 does not indicatesC or sM, step S1006 follows and a diffusion coefficient fixed typeerror diffusion process is executed to the quantization component. Thedata of the relevant quantization component of one line is formed instep S1007 and the processing routine advances to the process for thenext color. When the processes of all colors of the relevant line arefinished, the processing routine advances to the process for the nextline in step S1005.

[0067] Subsequently, effects of the present construction will bedescribed.

[0068] As already mentioned above, when the diffusion coefficientmodulation type error diffusion method is compared with the fixed typeerror diffusion method, since a processing load of the diffusioncoefficient fixed type error diffusion method is smaller than that ofthe former method, a processing speed is naturally higher.

[0069] In the embodiment, in the case of selecting one of a plurality oferror diffusion processes, the comparison is made every line on aquantization component unit basis. Thus, the processing load can belightened as compared with that in the case of performing the diffusioncoefficient modulation to the whole quantization component.

[0070] Subsequently, differences of the picture quality are compared.Explanation will be made with respect to an example of the cyan ink (C)of a large liquid droplet.

[0071] In the case of considering only a dot layout of the cyan ink,naturally, an image obtained by performing the diffusion coefficientmodulating process is better.

[0072] However, a case of expressing the actual image will be presumedas follows.

[0073] For example, in the case of expressing gradations in a range fromwhite to the highest density of cyan, as shown in FIG. 3, the apparatusis designed so that the image is formed only by the cyan ink (sC) of thesmall liquid droplet on the highlight side and, after the densityreaches a certain extent, the cyan ink (C) of the large liquid dropletis used.

[0074] Therefore, a density at the time when use of the cyan ink of theactual large liquid droplet is started is not equal to a value in thehighlight portion of the original image but is equal to a value near ahalftone of the original image in which the sufficient cyan ink of thesmall liquid droplet has already existed.

[0075] That is, in the real image, the dots in the use start portion ofthe cyan ink is inconspicuous. In other words, even if the diffusioncoefficient modulating process is not performed, a better image can beobtained.

[0076] As mentioned above, by using the quantizing method of theinvention, comparing the process in the embodiment with executing thediffusion coefficient modulating process to all of the quantizationcomponents, the better image can be formed while lightening the load ofthe quantizing process.

[0077] Although the embodiment has been described with respect to thecase of the cyan ink of the liquid droplets of the different sizes, theintention of the invention is not limited to such a combination. Theinvention can be adapted to a plurality of quantization components whosehighest densities which can be expressed in a similar color aredifferent.

[0078] At this time, the error diffusion process of the diffusioncoefficient modulation type is executed to the quantization componentwhose highest density which can be expressed is relatively low and theerror diffusion process of the diffusion coefficient fixed type isexecuted to the quantization component whose highest density which canbe expressed is relatively high.

[0079] Thus, the processing load can be reduced more and the betterimage can be maintained than those in the case of performing thediffusion coefficient modulation type error diffusion process to both ofthe quantization components.

[0080] As a combination of a plurality of quantization components whosehighest densities which can be expressed are different, in addition tothe difference between the sizes of the ink droplets mentioned above,there is a case where densities of dyes in the ink are different. Theinvention can be applied to such a condition. The invention can be alsoapplied to a case of a combination of both of the difference between thesizes of the ink droplets and the difference between the densities ofthe dyes in the ink. Also in those cases, similar effects can beobtained by executing the error diffusion process of the diffusioncoefficient modulation type to the quantization component whose highestdensity which can be expressed is relatively low and executing the errordiffusion process of the diffusion coefficient fixed type to the otherquantization component.

[0081] The embodiment has been described with respect to the case wherethe sizes of ink droplets are different at two levels. However, theinvention can be also applied to the case where the quantizationcomponents of a similar color are different at three or more levels dueto the difference among the sizes of the ink droplets or the densitiesof the dyes in the ink or a combination of them. In such a case, it isdesirable to execute the diffusion coefficient modulation type errordiffusion process to the quantization components from the quantizationcomponent whose highest density which can be expressed is lower.

[0082] For example, it is also possible to use a form in which when thesizes of the ink droplets are different at three levels and they are thedifferent quantization components, the diffusion coefficient modulationtype error diffusion process is executed only to the quantizationcomponent of the smallest liquid droplet. It is also possible to use aform in which the diffusion coefficient modulation type error diffusionprocess is executed to both of the quantization component of thesmallest liquid droplet and the quantization component of the secondsmallest liquid droplet.

[0083] That is, it is sufficient to execute the diffusion coefficientmodulation type error diffusion process to the component whose highestdensity which can be expressed is relatively low and execute thediffusion coefficient fixed type error diffusion process to thecomponent whose highest density which can be expressed is relativelyhigh.

[0084] Naturally, the diffusion coefficient modulation type errordiffusion process which is used in the embodiment is not limited tothose mentioned in the foregoing prior arts but incorporates all errordiffusion processes of the diffusion coefficient modulation type otherthan the processes using the fixed diffusion coefficients.

[0085] Second Embodiment

[0086] Subsequently, the second embodiment will be described withreference to FIG. 4. Although the first embodiment has been shown anddescribed with respect to the diffusion coefficient modulation typeerror diffusion process, a processing method in the case of a thresholdvalue modulation type error diffusion process is shown in the secondembodiment.

[0087]FIG. 4 is a flowchart showing an example of the second dataprocessing procedure in the image processing apparatus according to theinvention. The processes are executed by the quantizing unit 216 shownin FIG. 1. S4001 to S4007 denote processing steps, respectively.

[0088] First, the color component of the relevant line to be quantizedis inputted to the quantizing unit 216 (step S4001).

[0089] Subsequently, the quantization component of the relevant line isdiscriminated (step S4002). If it is determined that the quantizationcomponent of the relevant line is sC (or sM), step S4003 follows and thethreshold value modulation type error diffusion process is executed.

[0090] According to the threshold value modulation type error diffusionprocess, for example, a quantizing process is executed by using avariable threshold value determined on the basis of an input density ofa target pixel.

[0091] Data of the relevant quantization component of one line is formed(step S4004). When the data creation is finished, the processing routineadvances to the process for the next color (step S4005).

[0092] If it is determined that the discrimination result in step S4002is not sC (or sM), step S4006 follows and the threshold value fixed typeerror diffusion process is executed to the quantization component.

[0093] Data of the quantization component of one line is formed (stepS4007) and the processing routine advances to the next color.

[0094] After completion of the processes for all colors of the relevantline, step S4005 follows and the process for the next line is executed.

[0095] In a manner similar to the case of the first embodiment, when thethreshold value modulation type error diffusion process and thethreshold value fixed type error diffusion process are compared, aprocessing speed of the threshold value fixed type error diffusionprocess is higher because the load of the threshold value fixed typeerror diffusion process is smaller than that of the threshold valuemodulation type error diffusion process.

[0096] In the embodiment, in the case of selecting one of a plurality oferror diffusion processes, the comparison of the quantization componentunit is performed every line and the threshold value modulation is notperformed to all of the quantization components but the threshold valuemodulation type error diffusion process is executed only to apredetermined color. Thus, the load of the quantizing process can belightened.

[0097] Further, also in terms of the picture quality, as alreadydescribed in the foregoing embodiment, the apparatus is designed so thatthe image is formed on the highlight side only by the cyan ink (sC) ofthe small liquid droplet and, after the density reaches a certainextent, the cyan ink (C) of the large liquid droplet is used as shown inFIG. 3. Therefore, the density of the cyan ink of the actual largeliquid droplet at the time of starting to use it is not a value in thehighlight portion of the original image but becomes a value near thehalf tone in which a sufficient amount of cyan ink of the small liquiddroplet has already existed. In the actual image, consequently, the dotsat the density at timing near the start of the use of the cyan ink (C)are inconspicuous. Even if a slight delay of dot appearance occurs, agood image without noises and grainness can be obtained.

[0098] By using the quantizing method according to the second embodimentas mentioned above, the better image can be formed while lightening theload of the quantizing process as compared with the case of performingthe threshold value modulation type error diffusion process to all ofthe quantization components.

[0099] Although the second embodiment has been described with respect tothe case of using the cyan inks in which the sizes of liquid dropletsare different at two kinds in a manner similar to the case of the firstembodiment, the intention of the invention is not limited to such acombination.

[0100] Further, naturally, the invention can be applied to the case ofsimultaneously using the diffusion coefficient modulation type errordiffusion process and the threshold value modulation type errordiffusion process.

[0101] Third Embodiment

[0102] The third embodiment will now be described. The embodiment willbe explained with respect to the case of applying the invention to acorrelation type error diffusion process for a plurality of quantizationcomponents.

[0103] The correlation type error diffusion process for a plurality ofquantization components relates to the techniques disclosed inJP-A-H8-279920, JP-A-H11-10918, JP-A-H9-139841, JP-A-2002-171407, andthe like and relates to a processing method whereby in order to reduce,particularly, grainness of a middle density area of a color image, animage is formed so that the dots of the cyan (C) component and themagenta (M) component do not overlap mutually. That is, it relates to amethod whereby when one of those components is quantized, a value (inputvalue, output value, quantization error, etc.) regarding thequantization of the other component is reflected and the error diffusionprocess is executed.

[0104] The quantization components to be quantized are four colors ofcyan (C), magenta (M), yellow (Y), and black (K).

[0105]FIG. 5 is a flowchart showing an example of a third dataprocessing procedure in the image processing apparatus according to theinvention. The processes in this procedure are executed by thequantizing unit 216 shown in FIG. 1. S5001 to S5007 denote processingsteps, respectively.

[0106] First, the color component of the relevant line to be quantizedis inputted to the quantizing unit 216 (step S5001).

[0107] Subsequently, the quantization component of the relevant line isdiscriminated (step S5002). If it is determined that the quantizationcomponent of the relevant line is C or M, step S5003 follows and thecorrelation type error diffusion process is executed.

[0108] The diffusion coefficient modulation type error diffusion processand the threshold value modulation type error diffusion process havebeen implemented in a function of the correlation type error diffusionprocess and each effect has been reflected to a quantization result.

[0109] Unlike the case of the foregoing embodiments, as parameters suchas actual diffusion coefficient, threshold value, and the like, it ismore desirable to use parameters which have been optimized to thecorrelation type error diffusion process.

[0110] Data of the quantization component of one line is formed (stepS5004) and the processing routine advances to the next color.

[0111] If it is determined in step S5002 that the quantization componentis neither C nor M, step S5006 follows. In step S5006, the normal errordiffusion processes, that is, the diffusion coefficient fixed type errordiffusion process and the threshold value fixed type error diffusionprocess are executed to the quantization component.

[0112] Subsequently, the data of the quantization component of one lineis formed (step S5007) and the processing routine advances to the nextcolor. After completion of the quantization for all of the colors of therelevant line, step S5005 follows and the processing routine advances tothe next line.

[0113] The quantization components to which the correlation type errordiffusion process is applied are adapted to an area in a range from thelow density to a value near the middle density and to the cyan ink andthe magenta ink in which the grainness is visually conspicuous. They arenot applied to the yellow ink whose grainness is relatively low and theblack ink which is used in the high density portion (this is becausewith respect to the low density portion, the grainness is lightened byexpressing it by mixing the cyan ink, magenta ink, and yellow ink).

[0114] Similarly, by performing the diffusion coefficient modulationtype error diffusion process and the threshold value modulation typeerror diffusion process to an area in a range from the low density to avalue near the middle density and only to the cyan ink and the magentaink in which the grainness is visually conspicuous, a better image canbe obtained as compared with the case of executing the normalcorrelation type error diffusion process. The load of the quantizingprocess can be lightened by performing the normal error diffusionprocess to yellow and black.

[0115] Although the third embodiment has been described with respect tothe case of applying both of the diffusion coefficient modulation typeerror diffusion process and the threshold value modulation type errordiffusion process, the effects of the invention can be obtained even byapplying either of them in a manner similar to the cases of the firstand second embodiments mentioned above.

[0116] Although the cyan (C) and magenta (M) have been used asquantization components to which the correlation type error diffusionprocess is applied in the third embodiment, the invention is not limitedto such an example. That is, the quantization components to which thecorrelation type error diffusion process is applied are matched with thequantization components to which (both or either of) the diffusioncoefficient modulation type error diffusion process and the thresholdvalue modulation type error diffusion process are applied and thediffusion coefficient fixed type error diffusion process and thethreshold value fixed type error diffusion process are executed to otherquantization components.

[0117] Thus, the better image can be obtained while lightening the loadof the quantizing process as compared with the case of applying both oreither of the diffusion coefficient modulation type error diffusionprocess and the threshold value modulation type error diffusion processto all of the quantization components.

[0118] A construction of data processing programs which can be read outby the image processing apparatus according to the invention will bedescribed hereinbelow with reference to a memory map shown in FIG. 6.

[0119]FIG. 6 is a diagram for explaining the memory map of a storingmedium for storing various data processing programs which can be readout by the image processing apparatus according to the invention.

[0120] Although not particularly shown, information to manage a programgroup which is stored into the storing medium, for example, versioninformation, implementors, and the like are also stored. There is also acase where information which depends on the OS or the like on theprogram reading side, for example, icons or the like for identifying anddisplaying the programs are also stored.

[0121] Further, data which depends on the various programs is alsomanaged in the directory. There is also a case where a program toinstall the various programs into a computer or, if the installingprogram has been compressed, a program for decompressing it or the likeis also stored.

[0122] The functions shown in FIGS. 2, 4, and 5 in the embodiments canbe executed by a host computer on the basis of a program which isinstalled from the outside. In such a case, the invention is alsoapplied to a case where an information group including the programs issupplied to an output apparatus by a storing medium such as CD-ROM,flash memory, FD, or the like or from an external storing medium via anetwork.

[0123] Naturally, the objects of the invention are accomplished by amethod whereby the storing medium in which program codes of software torealize the foregoing functions of the embodiments have been recorded asmentioned above is supplied to a system or an apparatus and a computer(or a CPU or an MPU) of the system or the apparatus reads out theprogram codes stored in the storing medium and executes them.

[0124] In this case, the program codes themselves read out from thestoring medium realize the novel functions of the invention. The storingmedium in which the program codes have been stored constructs theinvention.

[0125] As a storing medium to supply the program codes, for example, aflexible disk, a hard disk, an optical disk, a magnetooptic disk, aCD-ROM, a CD-R, a magnetic tape, a non-volatile memory card, a ROM, anEEPROM, or the like can be used.

[0126] Naturally, the invention incorporates not only a case where acomputer executes the read-out program codes, so that the foregoingfunctions of the embodiments are realized but also a case where an OS(Operating System) or the like which is operating on the computerexecutes a part or all of actual processes on the basis of instructionsof the program codes and the foregoing functions of the embodiments arerealized by those processes.

[0127] Further, naturally, the invention incorporates a case where theprogram codes read out from the storing medium are written into a memoryprovided for a function expanding board inserted in a computer or afunction expanding unit connected to a computer and, thereafter, a CPUor the like provided for the function expanding board or the functionexpanding unit executes a part or all of actual processes on the basisof instructions of the program codes and the foregoing functions of theembodiments are realized by those processes.

[0128] Although the foregoing embodiments have been described withrespect to the construction in which the processes are realized by thesoftware for the sake of convenience, the intention of the invention isnot limited to such an example. They can be also realized by hardware.In addition to the above effects, a new effect such that as comparedwith the case of realizing the prior arts by hardware as it is, they canbe realized by hardware of a small scale and it is possible tocontribute to the reduction in costs of the whole system can be alsoobtained.

[0129] The invention is not limited to the foregoing embodiments butvarious modifications (including organic combinations of theembodiments) are possible on the basis of the spirit of the invention,and they are not excluded from the scope of the invention.

[0130] Although the embodiments have been described with respect to theexample in which the image data is printed onto the recording paper, theinvention can be also applied to image processing apparatuses in variouselectronic equipment using paper, cloth, leather, nonwoven fabric cloth,an OHP sheet, or the like, and further, a medium to be recorded such asmetal or the like as a recording medium.

[0131] As equipment to which the image processing apparatus according tothe invention can be applied, office equipment such as printer, copyingapparatus, facsimile, and the like, displays such as CRT, LCD, and thelike, printed matter producing equipment, and the like can be mentioned.

[0132] Although the various examples and the embodiments of theinvention have been shown and described, naturally, those with ordinaryskill in the art will understand that the spirit and scope of theinvention are not limited to the specific explanation in thespecification but other various modifications are incorporated in theinvention.

[0133] According to the embodiments mentioned above, by lightening theprocessing load of the image processing unit, an image output in whichhigh picture quality and speed are maintained can be provided even in anenvironment in which the apparatus does not have a memory of a largeenough storing capacity and a high-speed CPU.

[0134] An image output in which even in various image data processingenvironments, a load to the main body engine unit is minimized whileflexibly coping with them and high picture quality and speed aremaintained can be provided. Particularly, a printer system of areasonable price can be realized while lightening the load of thequantizing process in the photodirect printer system and minimizing thechange in printer engine unit.

[0135] According to the invention as described above, there is an effectsuch that the optimum error diffusion process is executed withoutincreasing the image data processing burden onto the multivalue imagedata which is inputted and the image data of high picture quality can beformed.

What is claimed is:
 1. An image processing apparatus for executing anerror diffusion process to multivalue image data consisting of aplurality of density components, comprising: first processing means forexecuting the error diffusion process by changing at least one of aquantization threshold value and a quantization diffusion coefficientwhich are used for said error diffusion process on the basis of a valueof said multivalue image data of the density components or a valuecalculated from said multivalue image data value; second processingmeans for executing the error diffusion process by setting thequantization threshold value and the quantization diffusion coefficientwhich are used for said error diffusion process into fixed values; anderror diffusion processing control means for making control to executethe error diffusion process to at least one color among said pluralityof density components by said first processing means and execute theerror diffusion process to other density components by said secondprocessing means.
 2. An apparatus according to claim 1, wherein saiderror diffusion processing control means executes the error diffusionprocess to the density components of a similar color among saidplurality of density components by executing the error diffusion processto the density component whose highest density which can be expressed islow by said first processing means and executing the error diffusionprocess to the density component whose highest density which can beexpressed is high by said second processing means.
 3. An apparatusaccording to claim 1, wherein said first processing means is an errordiffusion process for executing quantization on the basis of informationof the other density components among said plurality of densitycomponents.
 4. A print control apparatus for executing an errordiffusion process to multivalue image data consisting of a plurality ofdensity components, comprising: first processing means for executing theerror diffusion process by changing at least one of a quantizationthreshold value and a quantization diffusion coefficient which are usedfor said error diffusion process on the basis of a value of saidmultivalue image data of the density components or a value calculatedfrom said multivalue image data value; second processing means forexecuting the error diffusion process by setting the quantizationthreshold value and the quantization diffusion coefficient which areused for said error diffusion process into fixed values; and errordiffusion processing control means for making control to execute theerror diffusion process to at least one color among said plurality ofdensity components by said first processing means and execute the errordiffusion process to other density components by said second processingmeans.
 5. An apparatus according to claim 4, wherein said errordiffusion processing control means executes the error diffusion processto the density components of a similar color among said plurality ofdensity components by executing the error diffusion process to thedensity component whose highest density which can be expressed is low bysaid first processing means and executing the error diffusion process tothe density component whose highest density which can be expressed ishigh by said second processing means.
 6. An apparatus according to claim4, wherein said first processing means is an error diffusion process forexecuting quantization on the basis of information of the other densitycomponents among said plurality of density components.
 7. An imageprocessing method of executing an error diffusion process to multivalueimage data consisting of a plurality of density components, comprising:a first processing step of executing the error diffusion process bychanging at least one of a quantization threshold value and aquantization diffusion coefficient which are used for said errordiffusion process on the basis of a value of said multivalue image dataof the density components or a value calculated from said multivalueimage data value; a second processing step of executing the errordiffusion process by setting the quantization threshold value and thequantization diffusion coefficient which are used for said errordiffusion process into fixed values; and an error diffusion processingcontrol step of making control to execute the error diffusion process toat least one color among said plurality of density components by saidfirst processing step and execute the error diffusion process to otherdensity components by said second processing step.
 8. A method accordingto claim 7, wherein in said error diffusion processing control step, theerror diffusion process is executed to the density components of asimilar color among said plurality of density components by executingthe error diffusion process to the density component whose highestdensity which can be expressed is low by said first processing step andexecuting the error diffusion process to the density component whosehighest density which can be expressed is high by said second processingstep.
 9. A method according to claim 7, wherein said first processingstep is an error diffusion process for executing quantization on thebasis of information of the other density components among saidplurality of density components.
 10. A print control method of executingan error diffusion process to multivalue image data consisting of aplurality of density components, comprising: a first processing step ofexecuting the error diffusion process by changing at least one of aquantization threshold value and a quantization diffusion coefficientwhich are used for said error diffusion process on the basis of a valueof said multivalue image data of the density components or a valuecalculated from said multivalue image data value; a second processingstep of executing the error diffusion process by setting thequantization threshold value and the quantization diffusion coefficientwhich are used for said error diffusion process into fixed values; andan error diffusion processing control step of making control to executethe error diffusion process to at least one color among said pluralityof density components by said first processing step and execute theerror diffusion process to other density components by said secondprocessing step.
 11. A method according to claim 10, wherein in saiderror diffusion processing control step, the error diffusion process isexecuted to the density components of a similar color among saidplurality of density components by executing the error diffusion processto the density component whose highest density which can be expressed islow by said first processing step and executing the error diffusionprocess to the density component whose highest density which can beexpressed is high by said second processing step.
 12. A method accordingto claim 10, wherein said first processing step is an error diffusionprocess for executing quantization on the basis of information of theother density components among said plurality of density components. 13.A computer-readable storing medium which stores an image processingprogram for executing an error diffusion process to multivalue imagedata consisting of a plurality of density components, wherein saidprogram comprises: a first processing step of executing the errordiffusion process by changing at least one of a quantization thresholdvalue and a quantization diffusion coefficient which are used for saiderror diffusion process on the basis of a value of said multivalue imagedata of the density components or a value calculated from saidmultivalue image data value; a second processing step of executing theerror diffusion process by setting the quantization threshold value andthe quantization diffusion coefficient which are used for said errordiffusion process into fixed values; and an error diffusion processingcontrol step of making control to execute the error diffusion process toat least one color among said plurality of density components by saidfirst processing step and execute the error diffusion process to otherdensity components by said second processing step.
 14. A mediumaccording to claim 13, wherein in said error diffusion processingcontrol step, the error diffusion process is executed to the densitycomponents of a similar color among said plurality of density componentsby executing the error diffusion process to the density component whosehighest density which can be expressed is low by said first processingstep and executing the error diffusion process to the density componentwhose highest density which can be expressed is high by said secondprocessing step.
 15. A medium according to claim 13, wherein said firstprocessing step is an error diffusion process for executing quantizationon the basis of information of the other density components among saidplurality of density components.
 16. A computer-readable storing mediumwhich stores a print control program for executing an error diffusionprocess to multivalue image data consisting of a plurality of densitycomponents, wherein said program comprises: a first processing step ofexecuting the error diffusion process by changing at least one of aquantization threshold value and a quantization diffusion coefficientwhich are used for said error diffusion process on the basis of a valueof said multivalue image data of the density components or a valuecalculated from said multivalue image data value; a second processingstep of executing the error diffusion process by setting thequantization threshold value and the quantization diffusion coefficientwhich are used for said error diffusion process into fixed values; andan error diffusion processing control step of making control to executethe error diffusion process to at least one color among said pluralityof density components by said first processing step and execute theerror diffusion process to other density components by said secondprocessing step.
 17. A medium according to claim 16, wherein in saiderror diffusion processing control step, the error diffusion process isexecuted to the density components of a similar color among saidplurality of density components by executing the error diffusion processto the density component whose highest density which can be expressed islow by said first processing step and executing the error diffusionprocess to the density component whose highest density which can beexpressed is high by said second processing step.
 18. A medium accordingto claim 16, wherein said first processing step is an error diffusionprocess for executing quantization on the basis of information of theother density components among said plurality of density components. 19.An image processing program for executing an error diffusion process tomultivalue image data consisting of a plurality of density components,comprising: a first processing step of executing the error diffusionprocess by changing at least one of a quantization threshold value and aquantization diffusion coefficient which are used for said errordiffusion process on the basis of a value of said multivalue image dataof the density components or a value calculated from said multivalueimage data value; a second processing step of executing the errordiffusion process by setting the quantization threshold value and thequantization diffusion coefficient which are used for said errordiffusion process into fixed values; and an error diffusion processingcontrol step of making control to execute the error diffusion process toat least one color among said plurality of density components by saidfirst processing step and execute the error diffusion process to otherdensity components by said second processing step.
 20. A programaccording to claim 19, wherein in said error diffusion processingcontrol step, the error diffusion process is executed to the densitycomponents of a similar color among said plurality of density componentsby executing the error diffusion process to the density component whosehighest density which can be expressed is low by said first processingstep and executing the error diffusion process to the density componentwhose highest density which can be expressed is high by said secondprocessing step.
 21. A program according to claim 19, wherein said firstprocessing step is an error diffusion process for executing quantizationon the basis of information of the other density components among saidplurality of density components.
 22. A print control program forexecuting an error diffusion process to multivalue image data consistingof a plurality of density components, comprising: a first processingstep of executing the error diffusion process by changing at least oneof a quantization threshold value and a quantization diffusioncoefficient which are used for said error diffusion process on the basisof a value of said multivalue image data of the density components or avalue calculated from said multivalue image data value; a secondprocessing step of executing the error diffusion process by setting thequantization threshold value and the quantization diffusion coefficientwhich are used for said error diffusion process into fixed values; andan error diffusion processing control step of making control to executethe error diffusion process to at least one color among said pluralityof density components by said first processing step and execute theerror diffusion process to other density components by said secondprocessing step.
 23. A program according to claim 22, wherein in saiderror diffusion processing control step, the error diffusion process isexecuted to the density components of a similar color among saidplurality of density components by executing the error diffusion processto the density component whose highest density which can be expressed islow by said first processing step and executing the error diffusionprocess to the density component whose highest density which can beexpressed is high by said second processing step.
 24. A programaccording to claim 22, wherein said first processing step is an errordiffusion process for executing quantization on the basis of informationof the other density components among said plurality of densitycomponents.